1. Field of the Invention
This invention relates to a circuit for setting internal chip functions, and more particularly, to a circuit which can determine the mode of operation without dedicated configuration pins.
2. Description of Related Art
This circuit allows multiple configurations of an integrated circuit's operation with a minimum of external components. In the marketing of highly-integrated, application-specific integrated circuits, it is becoming increasingly difficult to target the needs of all customers. To successfully sell a product in today's competitive marketplace, a chip manufacturer must create a distinct "feel" to their product through its form and function.
One way of creating a distinct "feel" to a chip is to design in flexibility. An integrated circuit manufacturer can attempt to anticipate all of the demands of its customers by designing multiple modes of operation into their chip. These modes are usually selected through configuration pins which are dedicated to mode selection. Thus, some pins may be used for mode selection during normal operation of the chip. For highly integrated designs, the pins of a device are usually all used; there are very few which are unconnected. Pins are used as functional inputs and outputs during normal operations. Further, since there are only a limited number of pins on a given package, they come at a premium. It is sometimes hard to give up a pin for defining configurations. Hence it is desirable to be able to configure a device's operation without having to sacrifice a pin which could otherwise be used as a functional input or output.
In some chips, LEDs are used to indicate the status of the operational conditions. Accordingly, a mode selection pin may be configured to change the truth table of the LEDs, i.e., how they blink to indicate the various operational conditions. A configuration pin can allow the user to select an alternate display scheme by pulling this pin high or low. Then, the appropriate changes are made to the LED function. In this manner with two such mode selection pins, up to four distinct LED blink patterns can be selected.
A single LED can display three different states: on, off or blinking. Thus, a dual LED can correspondingly display a large amount of data using only a single pin of an integrated circuit (IC) as described in application Ser. No. 08/271,111, filed Jul. 6, 1994, herein incorporated by reference. Nevertheless, trying to visually interpret all the information present is difficult as it is possible to encode up to five states with a dual LED. Each user of the IC might also want to distinguish their product by changing the manner in which data is displayed to the user.
It is accordingly desirable to have an arrangement where multiple LED truth table schemes can be used with the integrated circuit device without reconfiguring an IC device or providing unique devices for the different situations.
It can be seen then that there is a need for multiple blink schemes designed into an IC.
It can be seen then that there is a need for a mode selection design which allows the user of the chip to differentiate his product from his competition and allow the IC manufacturer to use the pins available to him in an efficient manner.
There is accordingly a need to provide a system for operating with a number of selectable modes of operation and yet be efficient from a logic and circuitry perspective.